Diarrhea is a common manifestation of intestinal/ systemic
homeostatic altera-tion in neonatal calves, lambs, and kids. Neonatal diarrhea
may cause acute dehydration and death or lead to malnutrition and emaciation. Crypto-sporidium
parvum is highly infectious and highly resistant to inactivation in the
environment. There is no routinely successful form of therapy available.
There is also a zoonotic implication in humans handling the animals, especially
in immunocompromised humans.

Etiology and Pathogenesis: Neonatal calf diarrhea usually involves the
association of more than one pathogen. The most common implicated pathogens
are E. coli, rotavirus, coronavirus, and Cryptosporidium parvum. Cryptosporidium parvum (disease name Crypto-sporidiosis) is a protozoan
parasite transmitted by fecal-oral contamination. These protozoa invade the
apical surface (brush border) of the enterocyte in the distal small intestine
and proximal colon and form parasitophorus vacuoles where development occurs.
Infection results in crypt and submucosal inflammation, necrosis of microvilli,
villous atrophy, and decreased mucosal enzyme activity. This results in decreased
absorptive ability of the intestinal tract, fermentation of nutrients within
the lumen, and osmotic diarrhea.

Life cycle: Infection begins by ingestion of
oocysts from feces. These oocysts contain four sporozoites and initiate
infection following excystation. The organism replicates asexually and then
sexually to produce new oocysts that are shed into the environment in feces or
reinfect the host. The definitive hosts include many mammals such as cattle,
dogs, cats, and humans.

Epidemiology: C. parvum oocysts are commonly found in the feces
of healthy calves. The cause of diarrhea depends on multiple factors such as
the degree of virulence of the pathogenic strain, the presence of more than one
pathologic agent, and the success of passive transfer of colostral
immunoglobulins. Calves with low immunity are highly susceptible to
enteropathogenic infections leading to severe and often fatal diarrhea. Also,
the lack of specific antibodies in the dam and the use of specific vaccines may
interfere in the immunoglobulin transfer to the calf. Stress factors, poor
environmental conditions, exposure to contaminated maternal feces as well as
feces from healthy calves, and inappropriate diet also increase the risk for
disease. Transmission is by fecal-oral contact and fecal aerosol.

Diagnostics: Fecal samples from untreated calves should be submitted
during early diarrheic stages. Sugar flotation can be performed to identify
the oocysts. Bacteriology and virology cultures can be performed to verify the
presence of other agents. The microbiologic interpretation may be difficult
because of mixed infection and because some potential enteropathogens are
commonly present in healthy calves. Ideally, live representative calves should
be presented for necropsy examination so that fresh intestinal sections can be
prepared to identify the presence of organisms at the surface of epithelial
cells.

Treatment: There is no effective chemo-therapeutic agent for routine
treatment of cryptosporidiosis, but supportive care is recommended. Paromycin
has been used with limited success in cats and human patients, but its efficacy
in other species has not been determined. Oral Bovine Serum concentrate has
been used in calves with experimentally induced cryptosporidiosis. Hunt and
Armstrong determined that there was a 33% reduction in the volume of diarrhea
at the peak of illness, 30% reduction in intestinal permeability, and enhanced
ideal crypt depth and villous surface area, as compared to untreated, infected
calves.

Prevention and control: Good hygiene during management of the entire herd is
important in reducing the incidence of cryptosporidiosis. Isolation of sick
calves to a separate area to reduce contamination is also important. The dam
and calf should be provided good nutrition, and administration of high quality
colostrum within the first six hours of birth helps reduce infection.